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    Author(s): Franz J. St JohnDiane DietrichCasey Crooks; Peter Balogun; Vesna de Serrano; Edwin Pozharski; James Kennon Smith; Elizabeth Bales; Jason Hurlbert
    Date: 2018
    Source: Biochemical Journal. 475(9): 1533-1551.
    Publication Series: Scientific Journal (JRNL)
    Station: Forest Products Laboratory
    PDF: View PDF  (8.0 MB)

    Description

    Glycoside hydrolase family 30 subfamily 8 (GH30-8) β-1,4-endoxylanases are known for their appendage-dependent function requiring recognition of an α-1,2-linked glucuronic acid (GlcA) common to glucuronoxylans for hydrolysis. Structural studies have indicated that the GlcA moiety of glucuronoxylans is coordinated through six hydrogen bonds and a salt bridge. These GlcA-dependent endoxylanases do not have significant activity on xylans that do not bear GlcA substitutions such as unsubstituted linear xylooligosacchar-ides or cereal bran arabinoxylans. In the present study, we present the structural and bio-chemical characteristics of xylanase 30A from Clostridium acetobutylicum (CaXyn30A) which was originally selected for study due to predicted structural differences within the GlcA coordination loops. Amino acid sequence comparisons indicated that this Gram-positive-derived GH30-8 more closely resembles Gram-negative derived forms of these endoxylanases: a hypothesis borne out in the developed crystallographic structure model of the CaXyn30A catalytic domain (CaXyn30A-CD). CaXyn30A-CD hydrolyzes xylans to linear and substituted oligoxylosides showing the greatest rate with the highly arabinofuranose (Araf)-substituted cereal arabinoxylans. CaXyn30A-CD hydrolyzes xyloo-ligosaccharides larger than xylotriose and shows an increased relative rate of hydrolysis for xylooligosaccharides containing α-1,2-linked arabinofuranose substitutions. Biochemical analysis confirms that CaXyn30A benefits from five xylose-binding subsites which extend from the −3 subsite to the +2 subsite of the binding cleft. These studies indicate that CaXyn30A is a GlcA-independent endoxylanase that may have evolved for the preferential recognition of α-1,2-Araf substitutions on xylan chains.

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    Citation

    St John, Franz J.; Dietrich, Diane; Crooks, Casey; Balogun, Peter; de Serrano, Vesna; Pozharski, Edwin; Smith, James Kennon; Bales, Elizabeth; Hurlbert, Jason. 2018. A plasmid borne, functionally novel glycoside hydrolase family 30 subfamily 8 endoxylanase from solventogenic Clostridium . Biochemical Journal. 475(9): 1533-1551.

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    Keywords

    Glucuronoxylan, arabinoxylan, andoxylanase, glycoside hydrolase family 30, GH30, lignocellulose pretreatment, protein structure, PDB Code: 5CXP

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https://www.fs.usda.gov/treesearch/pubs/57573